Hong Kong was confirmed by the World Health Organisation (WHO) to have achieved measles-free status in 2016. But the disease has returned to the spotlight after a surge in cases was reported in the Japanese prefecture of Okinawa as well as in Taiwan – both popular travel destinations among Hongkongers. City health officials have asked people who are at risk, such as unvaccinated young children, to avoid visiting the affected areas.

What is measles, and why is it a concern?

Measles is a highly infectious disease caused by the measles virus. Infected patients first have symptoms such as a fever, runny nose and white spots inside the mouth, followed by a red, blotchy skin rash that can spread over the body and persist for up to three weeks. In severe cases, the lungs, gastrointestinal tract and brain can be affected, leading to serious consequences including death.

The disease can be transmitted through the air, such as by coughing and sneezing, or via direct contact with an infected person’s nasal or throat secretions.

Despite the availability of a vaccine, measles remains one of the leading causes of death among young children globally. According to the WHO, about 90,000 people around the world died from the disease in 2016, most of them children under the age of five.

When did the latest measles outbreak happen, and how widespread is the disease in the region?

The recent outbreak of measles in Okinawa began in late March after an infected man from Taiwan visited the Japanese prefecture. As of Tuesday, there were 85 measles cases recorded in Okinawa. Experts believe it spread through community transmission, and not only within hospitals, as recent cases were found to have no links to other confirmed cases, and new cases were seen in different parts of the prefecture.

Cases were also recorded in other parts of Japan, such as Aichi prefecture, where 13 cases had been reported by Tuesday.

In Taiwan, 24 measles cases had been recorded, but there has been no evidence of community spread there yet.

Citing data from overseas authorities, Hong Kong health officials said hundreds of measles cases were recorded elsewhere in the world earlier this year. For example, 855 cases were reported in the Philippines, 689 in mainland China and 884 in Greece in the first two months of this year.

How have the outbreaks affected Hong Kong?

Local health authorities believe it is unlikely the city will witness a measles outbreak, as most Hongkongers are immune to the infection. This year, Hong Kong has seen just six cases. They included three cases in March and three in April. In one case, a 46-year-old expat spent more than a month in Thailand before he developed symptoms about two weeks ago.

However, travel plans for hundreds of Hongkongers have been affected, as some tours to Okinawa organised by local agencies have been cancelled over fears about the outbreak.

How protected are Hongkongers against measles?

According to a Department of Health immunisation coverage survey of preschoolers in 2015, more than 95 per cent of surveyed children were vaccinated against measles. Separate studies by the department showed that more than 98 per cent of the studied population also had antibodies against the disease.

Measles vaccinations were first introduced under the city’s childhood immunisation programme in 1967. From 1996, the vaccines were offered in two doses. Under the programme, the measles vaccine is administered in combination with the mumps and rubella vaccines and called the MMR vaccine; it is given to children at the age of one. The second dose is provided to children in Primary One.

It usually takes about two weeks for a person to develop antibodies and protection against the virus after vaccination.

Wear a mask, wash your hands, and avoid crowded places

Dr Gabriel Choi, Medical Association

However, those who lack immunity, including children below the age of one who have not been vaccinated, as well as pregnant women who have not received the jabs, or developed protection from a previous infection, are at risk.

Should Hongkongers avoid going to areas where there is a measles outbreak?

Centre for Health Protection controller Dr Wong Ka-hing said the risk of travellers from the city getting infected with measles while travelling in affected places such as Okinawa was “low” given the high level of immunity among Hongkongers. However, young children who have not been vaccinated and non-immune women who are pregnant or planning to get pregnant should avoid visiting places where there is an outbreak.

How is measles prevented?

The Centre for Health Protection singled out vaccination as the “most effective preventive measure”. Dr Gabriel Choi Kin, president of the city’s Medical Association, advised the public to take preventive measures if they needed to visit places where an outbreak was under way.